Method of supplying electric furnaces with polyphase currents.



P. GIROD. METHOD OF SUPPLYING ELECTRIC FURNACES WITH POLYPHASE GURREN'IS.

APPLIGATION FILED AUG.24, 1910.

983,043, Patented Jan.31, 1911.

ATTORNEY;

METHOD OF SUPPLYING ELECTRIC FURNACES WITH POLYPHASE CUREEN'IS.

Uri Llflill.) ETATES PATENT OFFICE.

PAUL GIROD, OF UGINE, FRANCE.

Specification of Letters Patent.

Patented Jun. 31, 1911.

Application filed August 24, 1910. Serial No. 578,703.

To all whom it may concern:

Be it known that I, PAUL Ginon, a citizen of the Republic of Switzerland, residing at Ugine, Savoie, France, have invented certain new and useful lniproverrients in the Method of Supplying Electric l urnaces with Polyphaso Currents; and I do hereby declare the fOllOWll'lg to be. a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

It has heretofore been n'oposed to supply electric furnaces with polyphase currents, each phase being coi'niected directly with an electrode or group of electrodes. For example, the three distributing wires, 1, 2, 3, of a three-phase system have been respectively connected to three electrodes, or groups of electrodes i), a, (Z. In such case the potential diiierences existing between the several electrodes are the same. That is, the potential difference between 6 and c, is the same as that between 0 and d, and between (Z and Z). This system, which may be feasible when each of the electrodes, or each of the groups of electrodes, is similarly situated relatively to the bath, so that the resista11ces existing between the several electrodes are the same, is inadequate in the case of furnaces wherein the electrodes, or group of electrodes, are not so situated, as is the case, for example, in furnaces having one or more upper electrodes and the other electrode or electrodes in the hearth, or having a conducting hearth.

It is possible, by the interposition of transformers, to reproduce the above described conditions of equal voltages between the several electrodes, with or without a. change in voltage due to the transforma tion. Such a result is effected by providing two transformers of which the two primary terminals which at any instant are positive are connected to one of the three phases and the two terminals which at that instant are negative are connected respectively to the other two phases, or vice versa; and connecting the two like secondary terminals to one of the electrodes, or groups of electrodes, and the other two like secondary terminals to the other two electrodes, or groups of electrodes, respectively. Such an arrange ment, however, is, like the direct connection described above, inadequate for furnaces wherein the electrodes, or groups of electrodes, are not similarly situated with respect to the bath.

The present invention provides an ar rangement for overcoming this defect, and allows the current to be equally distributed among the several electrodes of an electric furnace when some of the electrodes are separated by a much higher resistance than other of the electrodes; and it consists essentially in inverting the terminals of one of the transfornmrs supplying the furnace so as to increase the potential difference between those electrodes which are separated by the greater resistance.

In the drawii'igs Figure l is a diagrammatic illustration of an electric furnace fed from a three phase system, with transformers interposed in such manner that the voltages between the several electrodes are the same. Fig. is a similar illustration of present invention, and Fig. 3 is a similar illustration of another arrangement canbodying the invention.

in Fig. l, a is an electric furnace of any suitable type, for example of the type clescribed in my French Patent No. 350,524 dated January t, 1905, and in certificates of addition to said patent, llo. et,829 dated May 22, 1905, and No. 7,008 dated December '4', 1906. The lower electrodes of the furnace are represented at I} and the upper. electrodes at c and (Z respectively, while the reference letter (1 indicates the bath of molten metal. The distribution wires of a three phase system are indicated in the figure and are numbered 1, 2, and respectively. It will be seen thatone ttillSfOllD-Gl has its primary 7 connected across the wires l-3, the lower terminal of the primary being connected to the wire 1 and the upper terminal to the wire 3. The other transformer has its primary g connected across the wires 1 2, its lower terminal being connected. to the wire 1, as is the lower terminal of primary f, and its upper terminal being con nected to the wire 2. The secondaries f and g of these two transformers have their lower terminals connected together and to the electrodes i), whereas their upper ter1ninals are connected respectively to the electrodes c and (Z. \Vith such a connection the voltage between the two electrodes 0 and d is the same as the voltage between the electrodes 0 and Z), and between the electrodes (Z and Z). The resistance between the electrodes 7) and (Z is the same as the resistaime between the electrodes 7) and 0, but is much I less than the resistance between the electrodes c and (Z since currents passing between these two electrodes would have to traverse two arcs in series. The result is that only a very small current, in comparison, would pass between the electrodes and d.

Tn accordance with the present; invention the voltage between. electrodes 1: and (Z is increased by inverting the terminals of one of the transformers (either the primary or secondary terminals). The connections are illustrated in l igs. 2 and 3. In Fig. 2 the primary terminals of the transformer are inverted, the upper terminal being connected to 1 and the lower terminal to 2-), while the upper terminals of primary (7 are connected as before, the upper to and the lower to 1. In Fig. 3 the priuuiry terminals of g are inverted, the upper one being connected to 1 and the lower to 2. while the terminals of primary f are connected as in Fig. l, the upper to 3 and the lower to 1. In either case the voltage between 7 and I: will be equal to the voltage between 7. and and the voltage between 6 and (Z is greater, being equal to the voltage between i; and 0 or b and d multiplied by B or 1.73. Thus, assuming that the secondaries ot' the transformers supply current at- 55 volts. there will exist between the electrodes Z) and c, and between the electrodes Z) and (Z, a dii'ferencc of potential of 55 volts and between and (Z a difference of potential 1.73 times greater, or approximately 95 volts. The intc-nsit of the current circulating between the electrodes c and d is consequently increased and in practice can be brought to approximately the same value. as the current which circulates between 6 and c, and between Z) and (7. l The same result may obviously be attained l by inverting the terminals of one of the secondaries, either f or g. The ratio of transformation may be one to one or wl'iatever other ratio may be required by the particular conditions of the installation. The same idea may be applied to six-phase, twelvephase and other polyphase systems by con necting the transformers in accordance with this invention. Of course, the number of electrodes would be increased or the number of furnaces connected to the system would be increased to utilize the greater number of phases, but the principle involved is an 0bvious modification of the system herein disclosed.

\Vhat I claim is:

.1. In a system for supplying current to an electric furnace having a plurality of electrodes and wherein the resistance between some of the electrodes is considerably greater than the resistance between others of the electrodes, supply conduch'n's carrying pol) phase currents, trz'insformers having their 6 out of contact with the fused metal. a threephase system of electrical supply, a pair ot a single-phase transformers having their primaries connected to different phases of the system and their secondaries cijinnccted to the said electrodes. the terminals of said transformers being relatively inverted and the secondary terminals being eonneclx-al to the electrodes in such order that the greater potential difference resultingfrom such inversion cxists between tee two upper electrodes.

S. in electric furnace l1lVl11' a lower electrode and a pair of upper electrodes held out of contact with the fused metal, a threephase system of electrical sup transformers having their nected to different phases of said :tem, the secondary of one transformer having one of its tern'iinals connected to the lower electrode and the other terminal connected to one of the upper electrodes and the secondary of the other transformer having one of its terminals connected to the lower clectrode and the other terminal connected to the other electrode. and the transformer terminals being relatively inverted, whereby a greater potential difference exists between the upper electrodes than between either upper electrode and the lower electrode.

In testimony whereof I affix my signature, in presence of two witnesses.

PAUL GIROD.

Witnesses LEON CAILLAT, BLACKERE CASTO N.

Correction in Letters Patent No. 983,043.

certified that in Letters Patent No. 983,043,

application of Paul Girod, of Ugine, France, for an improvement in It is hereby granted January 31,

1911, upon the Methods of Supplying Electric Furnaces with Polyphase Currents, an error appears in the printed specification requiring correction as follows:

before the word present Signed and sealed this 28th day of February, A. D., 1911.

[SEAL] C. C. BILLINGS, Acting Commissioner of Patents. 

